As a switch mechanism for effecting an emergency stop of a robot, a so-called deadman switch mechanism is known. Usually, the deadman switch mechanism is provided in a teaching operation panel which is connected to a robot controller. An operator holds the teaching operation panel, applies external operating force (pushing, holding or the like) to a handling member (lever, button, knob, handle or the like) of the deadman switch, and in that state, operates a robot manually.
FIGS. 1a and 1b show an example of basic structure of a switch switching mechanism used in a conventional deadman switch. FIG. 1a shows the switch switching mechanism to which external operating force is not applied, and FIG. 1b shows the switch switching mechanism to which external operating force is applied. In this example, a switch SW having a switch button SB as a movable contact element is provided in a teaching operation panel, and the switch button SB is brought into an ON- or OFF-state by a lever L.
With a known mechanism, the lever L which is a handling member is pivoted to turn around an axis AX, and biased in the direction denoted by an arrow A by appropriate biasing force. The force application face FS of the lever L to which external operating force is to be applied is exposed outside the teaching operation panel so that an operator can apply external operating force thereto (push the force application face by a finger tip).
The switch SW is normally open. When external operating force is not applied to the switch SW as shown in FIG. 1a, a known circuit including the switch SW does not send out an ON-signal. In order to operate a robot, the operator needs to push the force application face FS of the lever L to turn the lever L in the direction denoted by an arrow B to thereby push the switch button SB as shown in FIG. 1b. In that state, the circuit including the switch SW sends out an ON-signal to allow the robot to operate. Thus, the operator can operate the robot. Maintaining the state of FIG. 1b, the operator can continue operating the robot.
When the operator wants to stop operating the robot because he feels danger while operating the robot or for another reason, the operator stops pushing the lever L (the force application face FS) (for example, takes his finger tip off) to bring the switch SW back into the state of FIG. 1a to thereby prohibit the robot from operating.
The deadman switch mechanism in which one switch and one circuit are combined as described above has a serious problem in the way of safety. If trouble happens to a contact of such one switch or the circuit including such one switch, there is a risk that the robot may not be prohibited from operating though the operator stops pushing the lever L (the force application face FS), that is, the deadman switch may not do its most important function.
In order to solve the problem, (1) combining two switches and one circuit, or (2) combining two switches and two circuits has been already proposed. FIGS. 2a and 2b show an example of basic structure of a switch switching mechanism having two switches. FIG. 2a shows the switch switching mechanism to which external operating force is not applied, and FIG. 2b shows the switch switching mechanism to which external operating force is applied.
In this example, two switches SW1, SW2 having switch buttons SB1, SB2, respectively, are provided in a teaching operation panel. The switch button SB1 is brought into an ON- or OFF-state by a lever L1, and the switch button SB2 is brought into an ON- or OFF-state by a lever L2.
With known mechanisms, the levers L1, L2 are separately pivoted to turn around axes AX1, AX2, respectively, and biased in the direction denoted by an arrow A by appropriate biasing force. The force application faces FS1, FS2 of the levers L1, L2 to which external operating force is to be applied are exposed outside the teaching operation panel so that the operator can apply external operating force thereto (push the faces by finger tips). The levers L1, L2 are provided to handle the switches SW1, SW2, separately. When the lever L1 is pushed, the switch SW1 comes into an ON-state (without producing any effect on the switch SW2), and when the lever L2 is pushed, the switch SW2 comes into an ON-state (without producing any effect on the switch SW1).
In combining such two switches SW1, SW2 with one circuit, the following two modes, mode 1 and mode 2 are conceivable:
Mode 1; allowing a robot to operate on the condition that both of the switches SW1, SW2 are on (in FIG. 2b, "and" of "and/or" is effective).
Mode 2; allowing a robot to operate on the condition that at least one of the switches SW1, SW2 is on (in FIG. 2b, "or" of "and/or" is effective).
In mode 1, the operator needs to continue pushing the two levers L1, L2 simultaneously in order to operate the robot. This makes it very hard to handle other handling members of the teaching operation panel (for example, to handle a jog feeding button). Therefore, mode 2 is adopted, but if trouble happens to contacts of the switches or the circuit including the switches, mode 2 has the same risk as the above mentioned case in which one switch and one circuit are combined.
Specifically, there is a risk that due to some trouble, a contact or another part of the circuit may malfunction, so that the robot may not be prohibited from operating though the operator stops pushing the lever L1 or L2 (the force application face FS1 or FS2), that is, the deadman switch may not do its most important function.
In combining two switches SW1, SW2 with two separate circuits (referred to as "circuit 1" and "circuit 2"), respectively, the following two modes, mode 3 and mode 4 are conceivable as to how to deal with the outputs of the circuits:
Mode 3; allowing a robot to operate on the condition that both of the switches SW1 and SW2 are on (circuit 1 and circuit 2 are both in an ON-state) (in FIG. 2b, "and" of "and/or" is effective).
Mode 4; allowing a robot to operate on the condition that at least one of the switches SW1, SW2 is on (at least circuit 1 or circuit 2 is in an ON-state)(in FIG. 2b, "or" of "and/or" is effective).
In mode 3, same as in mode 1 described above, the operator needs to continue pushing the two levers L1, L2 simultaneously in order to operate the robot, so that it is very hard for the operator to handle other handling members of the teaching operation panel (for example, to handle a jog feeding button). Therefore, mode 4 is adopted, but same as mode 2 described above, mode 4 is not free from the above mentioned risk if trouble happens to contacts of the switches or the circuits including the switches.
Specifically, there is a risk that due to some trouble, a contact or another part of the circuits may malfunction, so that the robot may not be prohibited from operating though the operator stops pushing the lever L1 or L2 (the force application face FS1 or FS2), that is, the deadman switch may not do its most important function.
As described above, in the conventional deadman switch mechanisms, if trouble happens to a contact or another part of a circuit, the possibility that the minimum safety function will not be done is large.